Abstract: In this work we present results on the electrical and optical properties of nitrogen-doped hydrogenated amorphous germanium films (a-Ge:H). We used ammonia, NH3, as the doping gas for the films of a-Ge:H.
The a-Ge:H samples were prepared by rf-sputtering a c-Ge target in na Ar+H2+NH3 atmosphere. The NH3 partial pressure ranged from 2.7x10-6 to 1.4x10-4 mbar. It was the on1y deposition parameter varied between different deposition runs.
As the NH3 partial pressure in the chamber increases, the room-temperature dark conductivity (sRT) changes up-to 3 orders of magnitude. The activation energy of the dark conductivity decreases from 0.45 to 0.15 eV. These variations are the consequence of the incorporation of tetrahedrally bonded nitrogen atoms into the films (active doping).
We discuss the increase of topological disorder in the films produced by increasing NH3 partial pressures, determined from PDS (Photothermal Deflection Spectroscopy)
Moreover, spectroscopy measurements on the samples in the NIR-VIS region, show neither changes in the optical Tauc's gap nor in the E04 energy (photon energy corresponding to an absorption coefficient a = 104 cm-1). The content of hydrogen atoms bonded to Ge, around 6 % in alI the films, was determined from the integrated absorption of the Ge-H wagging vibration mode in the mid-infrared energy region. In these measurements absorption bands associated to the vibration modes H-N and Ge-N were not observed.
Finally, the results of active doping of the a-Ge:H network using ammonia are compared to those obtained using nitrogen as a doping gas